Force-sensing unit for measuring a belt tensile force acting on a seatbelt lock

ABSTRACT

Force-sensing unit for measuring a belt tensile force acting on a seatbelt lock, including a casing with an opening formed in a front side, and further including a moving anchor which is located in the casing and which protrudes through the opening and which has a stop that restricts the movement of the lug from the casing against an elastic support, and a sensor for registering the position of the moving anchor, whereby the casing can be attached between the seatbelt lock and an anchorage, characterized in that the elastic support is provided by a torsion spring supported on the anchor and on the casing on both sides of the anchor.

CLAIM FOR PRIORITY

[0001] This application claims priority to Romanian Application No. A2002-00990, which was filed on Jul. 16, 2002, which is hereby incorporated by reference.

TECHNICAL FIELD OF THE INVENTION

[0002] The invention relates to a force-sensing unit for measuring a belt tensile force acting on a seatbelt lock.

BACKGROUND OF THE INVENTION

[0003] To better protect occupants in an automobile it is necessary to measure the belt force of a person wearing a seatbelt. The data is processed and used during an accident to calculate the optimum triggering of belt tensioners and airbags.

[0004] The measuring device should therefore measure belt forces in the range 0-150 Newton with an accuracy of approximately +/−2.5%. Belt forces of up to 10,000 N can occur during standard operation. These must not cause damage to the measuring device or seatbelt lock. During an accident the belt force can rise to 20,000 N. The seatbelt lock and measuring device may, in this case, sustain permanent deformation damage but must not fail to operate properly.

[0005] A tried-and-tested principle for measuring forces is to measure displacement on a resilient component on which a force has impinged (spiral spring, torsion spring, coil spring, for example). An overload can easily be intercepted here if, after traveling beyond a path or angle specified in the design, the resilient component strikes a mechanical stop (step, edge).

[0006] U.S. Pat. No. 6,230,088 B1 discloses a force-sensing unit located between a seatbelt lock and an anchoring point secured to a vehicle's bodywork. However, this already known force-sensing unit for measuring a belt force is complex in its structure and difficult to install.

[0007] The invention, on the other hand, provides a simply structured and easily installable force-sensing unit that exhibits a sufficient degree of accuracy in measuring low-level forces.

[0008] In one embodiment of the invention, a force-sensing unit is provided which can be produced using standard components and is easy to install. A torsion spring is a simple component which supplies well reproducible values when bent within the elastic area.

[0009] In another embodiment of the invention, the torsion spring is formed by two arms advantageously designed to be an integral part of the anchor, can be manufactured economically. Furthermore, it is easy to detect after an accident whether the sensor has an anticipated zero point and consequently does not need replacing, which will save on repair costs. If the zero point has been shifted, meaning that a value exceeding 5 N, for example, is measured without the impact of a force, the force-sensing unit needs to be replaced.

[0010] In still another embodiment of the invention, a force-sensing unit is provided which can be easily secured to a seatbelt lock. The force-sensing unit can be manufactured separately and integrated later by the seatbelt lock manufacturer. This thus also makes it possible to subject the sensor to partial (gain and temperature) or complete (offset, gain, temperature) calibration prior to installation on the seatbelt lock or prior to delivery to the seatbelt lock manufacturer, which would simplify the manufacturing process as the seatbelt lock manufacturer will require minimal/no electronic calibration equipment.

[0011] Another advantage of the invention lies in the force-sensing unit's being easy to retrofit, with the possibility of securing it by simple means to a conventional seatbelt lock.

[0012] The force-sensing unit according to the invention can be used, for example, for optimum triggering of a belt tensioner and/or airbag.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Exemplary embodiments of the invention are described below with reference to the attached drawings, in which:

[0014]FIG. 1 shows a view of a force-sensing unit according to a preferred exemplary embodiment of the invention in the installed condition and without a case cover.

[0015]FIG. 2a shows a top view onto the force-sensing unit according to FIG. 1.

[0016]FIG. 2b shows a lateral view of the force-sensing unit according to FIG. 1.

[0017]FIG. 3 shows an exploded drawing of the perspective view according to FIG. 1.

[0018]FIG. 4 shows a cross-sectional view of the anchor shown in FIGS. 1 to 3.

[0019] The same reference numbers are used below for the same components in FIGS. 1 to 4.

DETAILED DESCRIPTION OF THE INVENTION

[0020]FIG. 1 shows a force-sensing unit 1 without the case cover that is located between a seatbelt lock 2 of conventional type and an anchorage 3. The anchorage 3 is conventionally connected to, for example, a vehicle's bodywork.

[0021] Force-sensing unit 1 has a casing 4 in which an anchor 5 is located in such a way as to be mobile. The part of anchor 5 which in the assembled condition faces seatbelt lock 2 is designed as a lug 8 which protrudes through an opening 6 in the front casing wall 7 on the seatbelt lock side of casing 4 and which is designed with a flange-shaped stop 9 that restricts the mobility of anchor 5 from casing 4 in the direction of seatbelt lock 2, as can best be seen in FIG. 4.

[0022] Extending from stop 9 to the inside of the casing is a stud 10 on whose end a magnet 11 is located, as can best be seen in FIG. 2a. Elastically bendable arms of a torsion spring 12 extend from stud 10 toward both sides of casing 4. Stop 9, stud 10, and torsion spring 12 are preferably of integral design. Torsion spring 12 can also be designed as a separate component that protrudes through a clearance hole formed in stud 10.

[0023] Guide rollers 13 a and 13 b are attached with the ability to rotate to the end areas of torsion spring 12. Alternatively, the guide rollers can be replaced by rigid guide components made of material with a low coefficient of friction or they may be totally absent. Guide rollers 13 a and 13 b are directed into guides 14 a and 14 b which are formed in opposite side walls 15 a and 15 b of casing 4 and which terminate in stop surfaces for guide rollers 13 a and 13 b, as shown in FIGS. 1 to 3. Guides 14 a and 14 b are preferably designed as slots that are open toward anchorage 3 so that guide rollers 13 a and 13 b of torsion spring 12 can be easily introduced.

[0024] Lug 8 preferably has a hole 16, as can be seen in FIG. 3, for example, so it can be connected to seatbelt lock 2 by means of a rivet 17 when force-sensing unit 1 is in the assembled condition.

[0025] As can best be seen in FIG. 2, a sensor (a Hall sensor, for example) 18 is statically located in casing 4 of force-sensing unit 1. Through a change in a magnetic field caused by a movement of magnet 11 formed at the end of stud 10, Hall sensor 18 generates an electrical signal that can be conveyed via an electrical lead 19 to, for example, a control device (not shown) for driving a belt tensioner or airbag.

[0026] In its area facing away from front casing wall 7, casing 4 further includes a bolt 20 for securing a loop 21 that is permanently connected to anchorage 3.

[0027] To install force-sensing unit 1, first lug 8 of anchor 5 is inserted through opening 6 in front casing wall 7 and guide rollers 13 a, 13 b are introduced into guides 14 a, 14 b. The sensor, lead, and case cover are pre-fabricated units and are arranged on force-sensing unit 1. Lug 8 protruding from casing 4 is then secured, for example, to conventional seatbelt lock 2 by being riveted, for instance, or screwed or welded etc. at a location at which anchorage 3 is usually directly secured with seatbelt lock 2 when a force-sensing unit 1 is not used.

[0028] The dimensions of guide rollers 13 a, b and of stop 9 are preferably such that anchor 5 can be moved within a void area that is restricted in one direction by the guide rollers' making contact with the bearing surfaces of guides 14 a, 14 b and in the other direction by a stop component, not shown, formed, for example, in at least one of guides 14 a, 14 b, in order to prevent the magnet from making contact with the sensor.

[0029] When a seatbelt is put on and a locking mechanism, whose structure is known per se and which is included in seatbelt lock casing 2, is fastened, a slight belt force takes effect. The effect of this belt force is that the guide rollers of torsion spring 12 will make reliable contact with the bearing surfaces of guides 14 a, 14 b. If the belt force is further increased, anchor 5 will be withdrawn from opening 6 with increasing deformation of torsion spring 12 until stop 9 of anchor 5 makes contact with the inside of front wall 7 of casing area 4 in order to obviate impermissibly extensive deformation of or damage to torsion spring 12.

[0030] It is possible with the force measuring device according to the invention to reliably determine whether a belt has been properly put on (guide rollers stopped against bearing surfaces and no or only slight deformation of the torsion spring). Within the operating range of the force-sensing device (elastic deformation area of the torsion spring) it is possible to accurately measure forces of up to, for instance, around 10,000 N. Forces in excess of this that will occur during a crash are taken up by the stop. The course over time of the build-up of force within the operating range yields information about an imminent crash that can be used to control a belt tensioner or airbag. Damaging of the force-sensing device can therefore be detected from its zero shift (guide rollers making contact with the bearing surfaces without the effect of force).

[0031] The invention described in detail above is not restricted to the preferred exemplary embodiment cited, but is simply intended to serve as an example and in no way limits the scope of the invention. For example, an optical sensor can be employed instead of a Hall sensor to determine the position of the anchor. A magnet would not be necessary in this case. 

What is claimed is:
 1. A force-sensing unit for measuring a belt tensile force acting on a seatbelt lock, comprising: a casing with an opening formed in a front side, and further including a moving anchor which is located in the casing and which protrudes through the opening and which has a stop that restricts movement of a lug from the casing against an elastic support; and a sensor for registering a position of the moving anchor, wherein the casing is configured to be attached between the seatbelt lock and an anchorage, such that the elastic support is provided via a torsion spring that is supported on the anchor and on both sides of the anchor on the casing.
 2. The force-sensing unit according to claim 1, wherein the torsion spring has two arms proceeding from the anchor that face in opposite directions and extend transversely to a direction of movement of the anchor and whose ends facing in opposite directions are directed into guides which are formed on walls of the casing and run approximately parallel to the movement of the anchor and which terminate in bearing surfaces, wherein the ends of the arms of the torsion spring make contact with the bearing surfaces when the anchor is shifted and, when the anchor is shifted further, stop of the anchor makes contact with the inside of the casing with elastic deformation of the arms.
 3. The force-sensing unit according to claim 2, wherein the guides are slots which are open at an end facing away from the bearing surfaces.
 4. The force-sensing unit according to claim 2, wherein the torsion spring has guide rollers that are directed into guides.
 5. The force-sensing unit according to claim 1, wherein the torsion spring is designed as an integral part of the anchor.
 6. The Force-sensing unit according to claim 1, wherein the force-sensing unit is configured to be secured via a lug protruding through the casing on the seatbelt lock and via a bolt on the casing to an anchorage.
 7. The force-sensing unit according to claim 1, wherein a lug, stop and stud are formed in an integrated manner.
 8. The force-sensing unit according to claim 1, wherein the anchor carries a magnet and the sensor is a Hall sensor in order to supply an electrical signal corresponding to the position of the anchor. 